ABSENCE OF COUNTERCURRENT EXCHANGE OF OXYGEN, CARBON DIOXIDE, HYDROGEN IONS OR GLUCOSE BETWEEN THE ARTERIAL AND VENOUS BLOOD IN THE SPERMATIC CORDS OF RAMS AND TWO MARSUPIALS (MACROPUS EUGENII AND MEGALEIA RUFA)
In the intermingled arteries and veins of the retia mirabilia leading to the swim-bladders of fishes (see Enns, Douglas & Scholander, 1967; Berg & Steen, 1968) O2 and CO2 are transferred from one vessel to another. It has also been suggested that O2 may pass between the arterial and venous blood in the spermatic cord (Cross & Silver, 1962) but the similar O2 saturation of haemoglobin in blood from the femoral and testicular arteries of rams did not support this idea (Setchell & Waites, 1964). However, in most marsupials, the internal spermatic artery breaks up into many branches in the spermatic cord and these branches are interspersed among a similar number of veins (Harrison, 1948, 1949; Barnett & Brazenor, 1958). Countercurrent exchange of gases would be much more likely to occur with this anatomy than in the eutherian mammals in which the internal spermatic artery
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